A power system may comprise a variety of power sources, transmission lines, distribution centers and loads. The power sources, transmission lines, distribution centers and loads form a network, which is commonly known as the grid. The power sources are used to generate electric power. The power sources may be power generators utilize different technologies such as solar energy sources (e.g., solar panels), wind generators (e.g., wind turbines), combined heat and power (CHP) systems, marine energy, geothermal, biomass, fuel cells, micro-turbines and/or the like.
Power demand in a power system may vary within one day. The demand may peak during daytime and early evening hours and drop dramatically during the night. On the other hand, due to the nature of renewable energy, the outputs of some power sources such as solar panels and wind turbines may vary considerably depending on uncontrollable natural factors such as wind strength and/or the like.
In order to provide reliable and stable power to critical loads, the power system may include a plurality of power storage units such as utility-scale energy storage systems, batteries and/or the like. The power storage units are designed so as to be capable of converting excess capacity into stored energy during off-peak hours and recovering the stored energy and converting it back to electricity during peak hours.
The energy storage units may be implemented as a rechargeable battery system, a compressed air energy storage system, a pumped storage hydroelectric system and/or the like. In a pumped storage hydroelectric system, during off-peak hours, the power generated by the power sources is greater than the power demand of the power system. The excess power may be utilized to pump water from a lower reservoir into an elevated reservoir. As such, excess electric energy is converted into potential energy and stored in the elevated reservoir. During peak hours, the water in the elevated reservoir is released to drive a water turbine. The water turbine is coupled to an electric generator, which converts potential energy back to electricity.
In a compressed air energy storage system, a motor driven compressor may compress atmospheric air into a storage container such as a tank, a cavern and/or the like during off-peak hours. As such, electric power is converted into pressure potential energy. On the other hand, during peak hours, the compressed air expands within an expansion apparatus in which the expanded air drives a mechanical component such as a shaft, which converts a reciprocating motion into a rotary motion. Such a rotary motion may be used to drive a power generator to generate electric power.